The poly-A tail in mRNA primarily affects which aspects?

• A. It serves as the coding sequence for amino acids
• B. It increases mRNA stability and enhances translation efficiency
• C. It directly participates in splicing
• D. It signals degradation by exonucleases

Answer: (B)

The poly-A tail mainly increases mRNA stability and translation efficiency. After transcription, a stretch of adenines is added to the 3’ end and binds poly(A)-binding proteins. These proteins couple with the cap-binding complex to circularize the mRNA, which makes ribosome recruitment and reinitiation more efficient, boosting how well the message is translated. The tail also shields the mRNA from 3’ to 5’ exonucleases, extending its lifespan so more protein can be produced over time. It doesn’t encode amino acids, and splicing is carried out before polyadenylation, so the tail isn’t directly involved in splicing. While shortening of the tail can lead to decay, its primary role is enhancing stability and translation, not signaling degradation.